1. Field of the Invention
The present invention relates to a color wheel driving motor and a DLP projector (digital-light-processing projector) provided with the color wheel driving motor.
2. Description of the Related Art
Conventionally, there are many different kinds of image projection systems. Among them, a DLP (Digital-Light-Processing) (registered trademark) projector has become a dominant stream of digital projectors because it has advantages of high intensity, high durability, small size, and the like. The DLP projector includes a color wheel which is fixed to a color wheel driving motor. When the DLP projector is in operation, it is necessary to detect the rotation position of the motor. In a motor disclosed in, e.g., Chinese Patent No. 1179344, the position of a rotating body is detected by allowing an inductor to detect the magnetic fluxes of a rotor magnet. As shown in FIGS. 1 and 2, the motor includes a rotor yoke 103 formed into a shallow cup shape. The rotor yoke 103 has a flange portion 103a integrally formed with the peripheral portion thereof. A window portion 103b in the form of a cutout having a specified width is formed in a portion of the flange portion 103a. A shaft 109 is attached to the rotor yoke 103 so as to pass through the center of the rotor yoke 103. A rotor magnet 108 having a ring shape and an endless shape is stuck to and arranged on the inner circumference of the flange portion 103a. The rotor magnet 108 is alternately magnetized with S-poles and N-poles at a regular interval along the circumferential direction. A portion of the rotor magnet 108 is passed through the window portion 103b and is exposed outward of the rotor yoke 103. As shown in FIG. 3, an inductor 107 is arranged near the outer circumference of flange portion 103a. For that reason, if the rotor yoke 103 of the motor makes rotation, the rotor magnet 108 facing outward through the window portion 103b is rotationally moved away from or toward the inductor 107. If the rotor magnet 108 exposed from the window portion 103b is moved away from the inductor 107, the inductor 107 seldom receives the magnetic fluxes of the rotor magnet 108. Thus, the induced voltage is equal to nearly zero. However, if the rotor magnet 108 facing the window portion 103b is moved toward the inductor 107, the inductor 107 receives the magnetic fluxes of the rotor magnet 108. The induced voltage of the inductor 107 has a value proportional to the time-dependent variation of the magnetic fluxes. A motor rotation index signal can be obtained by processing a magnetic flux detection output value of the inductor 107.
However, the motor as disclosed in Chinese Patent No. 1179344 suffers from the following technical problems. In the motor, a portion of the rotor magnet 108 is exposed from the window portion 103b. Therefore, an unbalance is generated in the rotor yoke 103. Since the window portion 103b is formed in the rotor yoke 103, the magnetic fluxes of the rotor magnet 108 are leaked through the window portion 103b, thereby worsening the characteristics of the motor. When the rotor magnet 108 is fixed to the rotor yoke 103, an adhesive agent cannot be coated on the entire outer circumferential surface of the rotor magnet 108. This may increase vibrations and noises. When assembling the rotor magnet 108 and the rotor yoke 103, a mark for identifying a border of magnetic poles needs to be attached to the rotor magnet 108, thereby exposing the border of the magnetic poles of the rotor magnet 108 from the window portion 103b. This may reduce the efficiency of an assembling work. In case of employing this method, there is a need to expose the border of the magnetic poles of the rotor magnet 108 from the window portion 103b and to bring the border of the magnetic poles into alignment with a color border of a color wheel.
Accordingly, a need has existed for a motor capable of solving the technical problems noted above.